A major drawback in the study of central nervous system aging has been the lack of an adequate neuronal model for the correlation of morphological, physiological and biochemical alterations with age. The studies proposed here will investigate two functionally related systems of neurons (the LHRH system and the catecholamine system) in an attempt to provide such a model. The LHRH system lends itself to this study because it is readily identifiable, and known deficits in LHRH release accompany aging. In addition, functional manipulations with measurable physiological endpoints can be performed on the system. The catecholamine system, which modulates LHRH release, is also readily identifiable. Several techniques (immunocytochemistry, electron microscopy, radioimmunoassay and histofluorescence) will be used to study LHRH and catecholamine neurons in young adult female rats with normal estrous cycles, old animals in the various stages of reproductive senescence and old animals in which the estrous cycle has been restored by pharmacological means. The experiments proposed here should result in data which: 1) will allow correlation of structural changes in an aged neuron system with known functional deficits, 2) will indicate whether changes in LHRH secretion in the aged animal may result from possible pathological changes intrinsic to LHRH-producing neurons or to changes in the catecholamine system which in turn may influence LHRH, and 3) will provide information concerning the appropriateness of these systems as a model for neuronal aging.